X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fruntime%2Finterrupt.c;h=c516822562a94f19980216173a49506ec8a30a5d;hb=e48026257ea92807b2a5ee799476be198fc64dd6;hp=ecc3b840aece2b95340b589555e8be1f45971a69;hpb=a4e7c6bc705d739360dfaa9c3c652fd4a05d6c06;p=sbcl.git

diff --git a/src/runtime/interrupt.c b/src/runtime/interrupt.c
index ecc3b84..c516822 100644
--- a/src/runtime/interrupt.c
+++ b/src/runtime/interrupt.c
@@ -14,6 +14,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 
 #include <signal.h>
 #ifdef mach /* KLUDGE: #ifdef on lowercase symbols? Ick. -- WHN 19990904 */
@@ -213,6 +214,7 @@ undo_fake_foreign_function_call(os_context_t *context)
      * FREE_INTERRUPT_CONTEXT_INDEX? If so, we should say so. And
      * perhaps yes, unbind_to_here() really would be clearer and less
      * fragile.. */
+    /* dan (2001.08.10) thinks the above supposition is probably correct */
     unbind();
 
 #ifdef reg_ALLOC
@@ -565,22 +567,78 @@ interrupt_maybe_gc(int signal, siginfo_t *info, void *void_context)
  * noise to install handlers
  */
 
-/* Install a special low-level handler for signal; or if handler is
- * SIG_DFL, remove any special handling for signal. */
+/*
+ * what low-level signal handlers looked like before
+ * undoably_install_low_level_interrupt_handler() got involved
+ */
+struct low_level_signal_handler_state {
+    int was_modified;
+    void (*handler)(int, siginfo_t*, void*);
+} old_low_level_signal_handler_states[NSIG];
+
+void
+uninstall_low_level_interrupt_handlers_atexit(void)
+{
+    int signal;
+    for (signal = 0; signal < NSIG; ++signal) {
+	struct low_level_signal_handler_state
+	    *old_low_level_signal_handler_state =
+	    old_low_level_signal_handler_states + signal;
+	if (old_low_level_signal_handler_state->was_modified) {
+	    struct sigaction sa;
+	    sa.sa_sigaction = old_low_level_signal_handler_state->handler;
+	    sigemptyset(&sa.sa_mask);
+	    sa.sa_flags = SA_SIGINFO | SA_RESTART; 
+	    sigaction(signal, &sa, NULL);
+	}
+    }
+}
+
+/* Undoably install a special low-level handler for signal; or if
+ * handler is SIG_DFL, remove any special handling for signal.
+ *
+ * The "undoably" aspect is because we also arrange with atexit() for
+ * the handler to be restored to its old value. This is for tidiness:
+ * it shouldn't matter much ordinarily, but it does remove a window
+ * where e.g. memory fault signals (SIGSEGV or SIGBUS, which in
+ * ordinary operation of SBCL are sent to the generational garbage
+ * collector, then possibly onward to Lisp code) or SIGINT (which is
+ * ordinarily passed to Lisp code) could otherwise be handled
+ * bizarrely/brokenly because the Lisp code would try to deal with
+ * them using machinery (like stream output buffers) which has already
+ * been dismantled. */
 void
-interrupt_install_low_level_handler (int signal,
-				     void handler(int, siginfo_t*, void*))
+undoably_install_low_level_interrupt_handler (int signal,
+					      void handler(int,
+							   siginfo_t*,
+							   void*))
 {
     struct sigaction sa;
+    struct low_level_signal_handler_state *old_low_level_signal_handler_state =
+	old_low_level_signal_handler_states + signal;
+
+    if (0 > signal || signal >= NSIG) {
+	lose("bad signal number %d", signal);
+    }
 
     sa.sa_sigaction = handler;
     sigemptyset(&sa.sa_mask);
     sigaddset_blockable(&sa.sa_mask);
     sa.sa_flags = SA_SIGINFO | SA_RESTART;
 
-    sigaction(signal, &sa, NULL);
+    /* In the case of interrupt handlers which are modified more than
+     * once, we only save the original unmodified copy. */
+    if (!old_low_level_signal_handler_state->was_modified) {
+	struct sigaction *old_handler =
+	    (struct sigaction*) &old_low_level_signal_handler_state->handler;
+	old_low_level_signal_handler_state->was_modified = 1;
+	sigaction(signal, &sa, old_handler);
+    } else {
+	sigaction(signal, &sa, NULL);
+    }
+
     interrupt_low_level_handlers[signal] =
-	(ARE_SAME_HANDLER(handler,SIG_DFL) ? 0 : handler);
+	(ARE_SAME_HANDLER(handler, SIG_DFL) ? 0 : handler);
 }
 
 /* This is called from Lisp. */
@@ -635,6 +693,11 @@ interrupt_init(void)
     int i;
 
     SHOW("entering interrupt_init()");
+
+    /* Set up for recovery from any installed low-level handlers. */
+    atexit(&uninstall_low_level_interrupt_handlers_atexit);
+
+    /* Set up high level handler information. */
     for (i = 0; i < NSIG; i++) {
         interrupt_handlers[i].c =
 	    /* (The cast here blasts away the distinction between
@@ -644,5 +707,6 @@ interrupt_init(void)
 	     * 3-argument form is expected.) */
 	    (void (*)(int, siginfo_t*, void*))SIG_DFL;
     }
+
     SHOW("returning from interrupt_init()");
 }